1. Field of the Invention
The present invention relates to an imaging apparatus, including a solid-state imaging device containing a plurality of photoelectric conversion elements, and a color image data-generation unit that generates color image data represented by a luminance signal and color-difference signals, based on signals from the plurality of the photoelectric conversion elements.
2. Description of Related Art
A solid-state imaging device, having a plurality of photoelectric conversion elements including photoelectric conversion elements for detecting a luminance component and photoelectric conversion elements for detecting color components of R (red), G (green) and B (blue), has been proposed (see JP-A-2003-318375).
FIG. 3 is a schematic plan view of a solid-state imaging device. The solid-state imaging device 1b illustrated in FIG. 3 includes a two-dimensional regular array, along vertical and lateral directions, of plural photoelectric conversion elements, and FIG. 3 illustrates 16 photoelectric conversion elements in total, with 4 elements in the vertical direction by 4 elements in the lateral direction. In FIG. 3, each square block represents a photoelectric conversion element, and a symbol written therein indicates a light component to be detected by such photoelectric conversion element. A symbol “Y” indicates a luminance component of the light, while “R” indicate a red component of the light, “G” indicates a green component of the light, and “B” indicates a blue component of the light. In the following description, the photoelectric conversion element marked with Y is also referred to as the photoelectric conversion element Y, that marked with R as the photoelectric conversion element R, that marked with G as the photoelectric conversion element G and that marked with B as the photoelectric conversion element B.
The solid-state imaging device illustrated in FIG. 3 has such a structure that, on a light-receiving face of each of the plural photoelectric conversion elements of same characteristics, arrayed along vertical and lateral directions, one of a Y-filter, an R-color filter which transmits an R light, a G-color filter which transmits a G light, and a B-color filter which transmits a B light is provided. The Y-filters are provided, among the photoelectric conversion elements arrayed along vertical and lateral directions, on the photoelectric conversion elements arranged in positions of a checkerboard pattern, and the R-, G- and B-color filters are provided on the photoelectric conversion element in remaining positions in the checkerboard pattern.
Thus, in the solid-state imaging device 1b illustrated in FIG. 3, in even-numbered rows, filters are arranged in an order of “Y, G, Y, G, . . . ” on the individual light-receiving faces of the photoelectric conversion elements, and, in odd-numbered rows, a row containing an arrangement “R, Y, B, Y, R, . . . ” and a row containing an arrangement “B, Y, R, Y, B, . . . ” alternate, on the light-receiving faces of the photoelectric conversion elements.
The Y-filter is a filter having spectral characteristics correlated with luminance information and may be called a luminance filter, and an ND filter, a transparent filter, a white-colored filter and a gray-colored filter belong to this category, but a structure, in which no filter is provided on the light-receiving face of the photoelectric conversion element and the light directly enters the light-receiving face, may also be considered as a structure having a luminance filter.
Such solid-state imaging device is capable of detecting a luminance component and color components of the light separately, and can provide a resolving power for luminance not influenced by the color information, and a color reproducibility not influenced by the spectral characteristics of the luminance component.
Now, let us consider a case of generating color image data represented by a luminance signal and color-difference signals, based on the signals obtained from such solid-state imaging device.
In such case, an imaging apparatus equipped with the solid-state imaging device at first executes a signal interpolation process which interpolates, in each pixel position of the color image data to be generated and among necessary signals (4 signals including a luminance signal y and color signals r, g and b) in each pixel position of the color image data to be generated, the color signals and the luminance signal, not obtained from the photoelectric conversion element corresponding to each pixel position. For example, in a pixel position corresponding to the photoelectric conversion element Y in FIG. 3, color signals r, g and b are interpolated by the signals obtained from the photoelectric conversion elements around such photoelectric conversion element Y, and, in a pixel position corresponding to the photoelectric conversion element R in FIG. 3, signals y, g and b are interpolated by the signals obtained from the photoelectric conversion elements around such photoelectric conversion element R. Also in a pixel position corresponding to the photoelectric conversion element G in FIG. 3, signals y, r and b are interpolated by the signals obtained from the photoelectric conversion elements around such photoelectric conversion element G, and, in a pixel position corresponding to the photoelectric conversion element B in FIG. 3, signals y, r and g are interpolated by the signals obtained from the photoelectric conversion elements around such photoelectric conversion element B.
FIG. 4 illustrates a state after such signal interpolation process. In FIG. 4, each square block indicates a pixel position, and symbols in each block indicate signal components interpolated into such pixel position, wherein a symbol “y” represents a luminance signal, “r” represents a red signal, “g” a green signal and “b” a blue signal. As illustrated in FIG. 4, the luminance signal y and the color signals r, g and b are made present in each pixel position. Then the imaging apparatus generates, in each pixel position, color-difference signals Cr, Cb from the luminance signal y and the color signals r and b present therein, thereby forming color image data represented by the luminance signal y and the color-difference signals Cr, Cb.
The solid-state imaging device in the background art may utilize, as the luminance signal, not only the luminance signal y but also a luminance signal yrgb generated from the color signals r, g and b interpolated in each pixel position. In the case that the luminance filter is controlled to have such exact spectral characteristics as represented by a synthesizing equation of color signals r, g and b, there will be no difference in the color reproducibility of the luminance signal y and that of the luminance signal yrgb so that an image with satisfactory color reproducibility can be obtained even with the luminance signal y. However, when the spectral characteristics of the luminance filter y cannot be exactly controlled, the color reproducibility of the luminance signal y becomes inferior to that of the luminance signal yrgb, so that an image with satisfactory color reproducibility is difficult to generate in case of utilizing the luminance signal y. On the other hand, an image reproduction with the luminance signal yrgb provides a satisfactory color reproducibility, but the image resolution becomes inferior to the case of image reproduction with the luminance signal y.